Various kinds of frothing agents have been proposed in the past for making foams from thermosettable resins such as unsaturated polyesters. However, these frothing agents have not proven to be commercially useful. For this reason other methods such as polymerizing a water-in-resin emulsion followed by dewatering have been investigated.
Typical materials proposed in the art to stabilize unsaturated polyester foams are polyvinyl alcohol, ethyl cellulose, Pluronic surfactants, fatty acids, fatty alcohols, etc. A silicone oil is proposed in Belgium 638,308. An organosiloxane-oxyalkylene copolymer is suggested in FR 1,535,796. German 1,247,648 discloses preparation of polyester foams by mere mechanical frothing.
U.S. Pat. No. 3,511,788 teaches the use of certain silicone materials as foaming agents for organic liquids and plastisols. Modifications of the above silicone materials are taught in Dutch 72.09579 to be useful in making foams from unsaturated polyester resins. However, the modified silicones appear to be much more limited in their effectiveness than the scope of the Dutch patent would indicate.